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多媒體播放器之微控器系統設計

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圖 2-8  編譯軟體的 GPIO 設定      舉例本系統的SD記憶卡電源控制與卡片偵測應用電路,來說明GPIO的  基本輸入與輸出設定與使用。圖2-9的電路中,透過PA[2]控制P-MOSFET電  源開關,當輸出為低電位時,P-MOSFET導通並供給電源給SD記憶卡。若  輸出為高電位時,則關閉電源。      PA[8]用來偵測SD記憶卡是否插入或拔除,在記憶卡插槽中,有一根C/D  腳位元是用來偵測卡片狀態。當卡片插入插槽時,該C/D腳位會被拉到低電  位;相反的,當卡片拔除或沒有插好的狀況下,
圖 2-9 SD 記憶卡電源控制與插入偵測電路      圖2-10為本系統的電源控制與卡片偵測範常式式,使用GPIOA_IDR第8  位元的狀態,來偵測SD卡。使用GPIOA_ODR第2位元,來決定電源的供給。  程式名稱:check_sd_insert ( ),    SD_power_on ( )        SD_power_off  (  )  功能敘述:偵測卡片插入,打開 SD card 電源,    關閉 SD card 電源  輸    入:PA8 偵測卡片  輸    出:PA2 控制電
圖 2-16  編譯軟體的 TIM4 設定
圖 2-21  模擬 PWM 輸出波形
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